Panasonic tankless water heater will not start; display shows H01 and burner does not ignite.

Safety first: Turn OFF the unit, close the gas shutoff valve, and switch off the dedicated breaker before opening any covers. If you ever smell gas, stop immediately and contact your gas supplier or a licensed technician.

• 1. Reset the heater: Turn the power OFF for 2–3 minutes, then turn it back ON and try to start hot water again. Sometimes H01 is a temporary ignition lockout.
• 2. Check gas supply:
  • Verify the gas shutoff valve to the heater is fully open.
  • Confirm other gas appliances (stove, boiler) work normally. If not, there may be a supply issue.
• 3. Inspect air intake and exhaust:
  • Make sure the flue terminal and air intake grill are not blocked by debris, insects, or snow.
  • Clear any visible obstructions without disassembling the flue system.
• 4. Clean ignition electrode and flame rod (for qualified persons):
  • Remove the front cover.
  • Locate the burner assembly with the ignition electrode and flame rod.
  • Gently clean the metal tips with fine emery cloth or a non‑abrasive scouring pad to remove soot or oxidation.
  • Re‑assemble and test.
• 5. Check wiring to ignition components:
  • Inspect harnesses from the main control PCB to the ignition electrode and flame rod for loose or damaged connectors.
  • Reseat any loose plugs firmly.
• 6. If H01 persists: The main control PCB or gas valve assembly may be faulty. Do not attempt gas valve calibration yourself; contact an authorized Panasonic service center.